The adaptive optics scanning laser ophthalmoscope (AOSLO), developed by the Roorda Lab at UC Berkeley, is presently the world's only instrument able to present fully-stabilized bright stimuli to specific individual cones. Aim 1 extends this capability to a new instrument that will enable use by the research community at large. The ability to do careful psychophysics in the periphery, day after day, on the same targeted individual L, M, & S cones in the living human eye promises to usher in a new era of relating perception to physiology. This is clinically important for understanding the mechanisms of retinal diseases. This proposal has two components, the first is technological, to develop a flexible visual stimulator for studies of vision and the second is basic research that uses the device to characterize perception associated with cone and/or ganglion cell activations. Aim 1 extends the present tracking scanning laser ophthalmoscope (TSLO) without AO by the addition of three visible light sources and a pupil tracking system. The previous version of the TSLO was limited to the infrared (840 nm) beam running at maximum intensity for retinal imaging. Perceptually, this 840 nm light source is of limited brightness since only decrements may be presented. Thus, it is impossible to have visible single cone stimulation. With the visible wavelengths the enhanced TSLO (eTSLO) can use bright targets. In Aim 2, after we map out an array of cones identified by color class, we will reliably and repeatedly stimulate different single L, M and S cones while observers judge the color of the stimulus. Hofer et al (2005) have found that single cone stimulation near the fovea elicits a surprisingly wide variety of color percepts, but were unable to associate a specific cone with a particular color percept. This shortcoming is critical for testing the model of color vision proposed by Brainard et al (2008). Using the eTSLO technology, we will replicate the Hofer experiments but with identified cones to directly test the Brainard et al model of perceived color. Aim 3 focuses on using perceived color borders to begin identifying midget RGC's. The challenge is to devise more accurate methods to measure perceived color across the array of cones, 30 deg in the periphery. When perceived color changes as the stimulus moves from cone to cone it is indicative of crossing a RGC border. Small patches of cones associated with a single color percept likely indicate single RGC, whereas large patches indicate multiple RGC's with the same associated color percept. We expect to find different mechanisms in the near periphery, where cones of a single class are expected to innervate RGCs (Aim 2), versus the far periphery where multiple cones of different types activate the RGC centers (Aim 3). The proposed studies will demonstrate the capabilities of the eTSLO. Future studies involving independent stimulation of multiple cones will be able to address research questions extending from color to spatial vision in general. We envision eventual clinical deployment of the eTSLO for early detection of retinal diseases and evaluation of treatment outcomes.